1. Field of the Invention
The present invention relates to an optical waveform shaping device for shaping (or correcting) the waveform of an optical signal transmitted through a transmission path formed by an optical fiber or the like.
2. Description of the Related Art
In recent years, amounts of data transmitted or received have been greatly increasing in accordance with progress in data handling techniques. In order to transmit a vast amount of data, optical communications are more popularly used. Recently, optical fibers have been used, not only for basic or submarine transmission paths for transmitting optical signals over a long distance of a few hundred or a few thousand kilometers, but also for transmission paths for connecting firm offices or ordinary homes. A transmission path using optical fibers can reduce degradation of optical signals; however, degradation cannot be completely avoided. Therefore, when an optical signal is transmitted over a long distance, degradation of the optical signal occurs due to dispersion of each optical fiber, or the like.
Presently-available optical communication systems employ a dispersion-compensator for compensating dispersion of the optical fiber, or use optical fibers having improved performance or characteristics, so as to increase a possible transmission distance. However, such devices for increasing the transmission distance have their limits. In a recently-developed technique for further increasing the transmission distance, a waveform shaping process is performed before reproduction of the optical signal becomes impossible due to degradation of the signal. In the waveform shaping process, the optical signal transmitted through an optical fiber is once converted into an electrical signal and a waveform of the electrical signal is shaped (or corrected), and the electrical signal having the shaped waveform is again restored to an optical signal. This optical signal subjected to the waveform shaping process is transmitted through the optical fiber, thereby increasing the transmission distance. A detailed description of this technique may be found in Reference Document 1: Japanese Unexamined Patent Application, First Publication No. 2004-328304.
In the technique disclosed in Reference Document 1, the waveform shaping process is performed in which an optical signal, transmitted through an optical fiber, is once converted to an electrical signal, and the electrical signal is restored to an optical signal. In accordance with this process, the optical signal transmitted through the optical fiber can be restored to an optical signal before the transmission through the optical fiber.
However, in order to implement the waveform shaping process, expensive devices are necessary, such as a light source, an optical modulator, a light-receiving element enabling of high-speed operation, and high-speed digital and analog circuits, thereby increasing the cost relating to the entire transmission path. In addition, a device for implementing the waveform shaping process should be large-sized; thus, a problem may occur depending on the place where the device is installed.